EXPERIMENTAL AND THEORETICAL-STUDIES OF THE P-H BOND LENGTH AND STRETCHING MODE OF THE PHOSPHITE ANION

The P-H bond stretching frequencies of PHO3-2, HPHO3-, and H2PHO3 in a queous solution were measured by using FT-IR spectroscopy; the values obtained were 2322.29, 2387.67, and 2435.33 cm-1, respectively. Ab ini tio calculations were also performed on these molecules to compare the P-H bond lengths and stretching frequencies with experimental results . The average change in the P-H stretching frequency with bond length is found to be approximately 85 cm-1 /pm from the calculations and 11 cm-1/pm from experiment. Changes in the P-H bond length and stretching frequency are explained in terms of a molecular orbital picture, wher e the bond undergoes changes in energy and hybridization upon conversi on from one species to another. A test is made of two well-known empir ical relations between the bond length and the calculated force consta nt which showed that the relation given by Gordy is more consistent wi th experiment than the relation given by Badger. Finally, using NMR an d IR data, we show the exchange rate at room temperature (25-degrees-C ) of the acidic phosphite protons (bound to the oxygens) in an aqueous solution of HPHO3- and H2PHO3 is greater than 10(2) s-1 and less than 10(11) s-1.